It is known of in the art to make seats and frames separately, preferably in different materials, to later assemble them together. The interconnection of the seat and the frame is usually performed using rivets, bolts or screws passing through the seat so as to engage in relative holes made in the frame.
Such structures however present the drawback of requiring for their assembly riveting machines or staff specialised in assembling and connecting parts using the aforesaid means of connection.
For such reason, the seat elements of the prior art are normally assembled during the production phase so that the final product is a chair or stool already assembled and ready for use.
The pre-assembled structure has the disadvantage however of being cumbersome and unwieldy both during storage and relative transport.
Seat element structures in two separate parts having attachment devices and shaped couplings between relative counter-shaped portions of the frame and the seat are also known of in the art.
Such attachment devices and shaped couplings do not however ensure a safe and stable attachment over time: in other words with wear, and on account of the inevitable production tolerance, there is often unacceptable and annoying play between the seat and the frame.
Furthermore, the attachment devices of the known art tend to break during assembly and often ruin the seat by abrasion during assembly and subsequent dismantling phases.
The deterioration of the seat, even if on the under part of the seat and therefore not very visible, is not acceptable in the case in which the seat is, for example, upholstered in valuable material. Furthermore, in the case of an upholstered seat, the friction and damage of the covering may lead to jamming of the mechanism.